1. Field of the Invention
The present invention relates to an arrangement and to a method for monitoring and controlling a plurality of capacitances, which are connected in series.
2. Discussion of the Prior Art
A method for symmetrizing or balancing the condensers or capacitors of a condenser battery and a possible arrangement for that purpose are disclosed in European Patent Publication EP 1 406 143 A2. The condenser battery consists of a plurality of parallel-connected rows of presently individual condensers, which can be the so-called ultra-condensers. In order to be able to store the greatest possible amount of energy in such a condenser battery, it is important to uniformly charge all condensers of the battery; in effect, to charge uniformly and fully. This process is referred to as “symmetrizing”, or essentially balancing. In the event that there is applied to individual condensers, even if only for a short period of time, a condenser voltage which is in excess of a rated value, this will lead to a more rapid aging of this condenser. In an extreme case, this condenser must then be prematurely removed, which is complicated procedure.
Differing voltages which are applied to the individual condensers or capacitors which render the energy storage device inefficient, can be essentially traced back to the condenser properties; for example, to the replacement-series resistance and/or to the capacitance of the condenser. Moreover, parallel resistances can also be significant in that connection.
Accordingly, for this purpose, it becomes necessary to charge each individual condenser of a condenser battery to an upper voltage limit, and to protect it from an overload, which can lead to a destruction of the condenser. At an excessively high applied voltage, this can lead to a blowing-off of the electrolytes, which signifies a destruction of the condenser. However, by means of a diagnosis, it should be possible to early recognize as to whether a condenser is not capable of being fully operationally capable.
In the disclosure of EP 1 406 143 A2, for a monitoring of the charge condition of the condensers, there are prepared three voltage levels by means of a reference voltage source. At every condenser there is determined the condenser voltage and compared with the voltage levels. A correct charge of a condenser is indicated when the condenser voltage lies between the two lower voltage levels. A disorder of the condenser is indicated when the condenser voltage is greater than the highest voltage level. It is then only symmetrized or balanced when neither a correct charge nor a disorder is indicated. Through the intermediary of a bus system, there can, however, an evaluating unit can also be informed with regard to the error, so as to facilitate an immediate diagnosis of the failed condenser.
Similarly, EP 1 406 143 A2 discloses an arrangement, in which arranged in parallel with respectively two or more of the condensers of the condenser battery is a series circuit consisting of an ohmic resistance and a first transistor. Connected in parallel with the first transistor is at least one further transistor. The transistors are connected with an evaluating unit, whereby voltage tap-offs from the condensers are connected with the evaluating unit. The ohmic resistance of the series circuit, which is necessary for the symmetrizing serves as a discharge resistor, and, for example, can be a large wire-wound resistance. It can also have or also be a flat-bottom or surface resistance, an HSA resistance, or also a cement resistance. The transistors are, as a rule, so-called field-effect transistors. If required, upon occasion these field-effect resistors can be equipped with cooling elements.